1. Field of the Invention
Embodiments relate to a driver suitable for an organic electroluminescent display. More particularly, embodiments relate to a driver having two shift registers, but outputting three control signals, and associated methods.
2. Description of the Related Art
Various kinds of light and small-sized light emitting displays have been developed to supersede cathode ray tubes. Organic electroluminescent displays may have excellent light emitting efficiency, high luminance, excellent view angle, and a high response speed, and have thus been of great interest. Organic electroluminescent displays have been used as displays of portable information terminals, e.g., personal computers, handsets, personal digital assistants (PDAs), various kinds of information machines, etc.
An organic electroluminescent display may emit light by electrically exciting fluorescent or phosphorescent materials. The organic electroluminescent display may drive N×M organic electroluminescent display elements so as to display an image.
As illustrated in FIG. 1, the organic electroluminescent display element may include an anode of, e.g., indium tin oxide (ITO), an organic thin film and a cathode of, e.g., metal. The organic thin film may have a multi-layered structure including an emitting layer EML adapted to emit light by combining electrons and holes, an electron transport layer ETL adapted to transport electrons, and a hole transport layer HTL adapted to transport the holes. The organic thin film may include an electron injecting layer EIL adapted to inject the electrons and a hole injecting layer HIL adapted to inject the holes.
Techniques for driving the organic electroluminescent device may include a passive matrix (PM) technique and an active matrix (AM) technique employing a thin film transistor (TFT) or a metal oxide semiconductor field effect transistor (MOSFET). The PM technique may drive a light emitting cell by forming an anode intersecting a cathode and selecting a line. The AM technique is a driving technique that may connect the TFT and the capacitor to respective ITO pixel electrodes to maintain a voltage by employing charge stored by a capacitor. The AM technique may be a voltage programming technique or a current programming technique according whether a signal applied from a data driver is a current or a voltage.
A related art organic electroluminescent display may include pixels of each color in order to display various colors. A respective color may be represented by a combination of colors that emit light from the pixels. Each pixel may include a pixel circuit for displaying a red (R), a green (G) and a blue (B) color. A respective color may be produced by a combination of the R, G and B colors.
FIG. 2 illustrates a diagram of N×M pixel circuits of a related art voltage programming technique for driving an organic electroluminescent element.
Referring to FIG. 2, a driving transistor M1 may be connected to second, third and fourth switching elements S2, S3 and S4. The respective switching elements S2, S3 and S4 may receive a red light emitting control signal EmR[n], a green light emitting control signal EmG[n] and a blue light emitting control signal EmB[n] so as to supply a driving current to a red organic electroluminescent element OLEDR, a green organic electroluminescent element OLEDG, and a blue organic electroluminescent element OLEDB, respectively. An amount of current flowing through the driving transistor M1 may be controlled by a data voltage that is applied through a first switching element S1. A capacitor C1 may be connected between a gate and a source of the driving transistor M1 so as to maintain the applied voltage constant. The first switching element S1 may include a source connected to a data line Data[m] and a gate connected to a scan line Scan[n]. The circuit may include first and second power voltages VSS and VDD.
When the first switching element S1 is turned on in response to a scanning signal that is applied to the gate of the first switching element S1, a data voltage from the data line Data[m] may be applied to the gate of the driving transistor M1. Then, a driving current that corresponds to a voltage charged between the gate and the source of the driving transistor M1 may flow into the drain of the driving transistor M1. The red organic electroluminescent element OLEDR may emit red light via the driving current, when the second switching element S2 is turned on by the red light emitting control signal EmR[n]. The green organic electroluminescent element OLEDG may emit green light via the driving current, when the third switching element S3 is turned on by the green light emitting control signal EmG[n]. The blue organic electroluminescent element OLEDG may emit blue light via the driving current, when the fourth switching element S4 is turned on by the blue light emitting control signal EmB[n].
In order to drive the pixels, the respective pixel circuit may require a circuit for driving the organic electroluminescent element, a data driver for transferring a data signal, a scan driver for transferring a scan signal, and a light emitting control driver for transferring a light emitting control signal.
The light emitting control driver may include R, G and B light emitting control drivers for supplying each of the R, G and B light control signals, respectively. Since the R, G and B light emitting control drivers may each include a shift register, there may be a problematic increase in a size of the circuit due to many components.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.